Exposure history of the lunar meteorite, Elephant Moraine 87521

Abstract We report the noble gas concentrations and the 26 Al, 10 Be, 36 Cl, and 41 Ca activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for ~1 Ma at a depth of 1–5 g/cm 2 followed, not necessarily directly, by a second one for 26 Ma at ~565 g/cm 2 ; launch from the Moon less than 0.1 Ma ago; and arrival on Earth 15–50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent 2 . EET 87521 has a K Ar age in the range 3.0–3.4 Ga, which is typical for lunar mare basalts.